Dental pulp explants have been shown to form mature dentin with treated with synthetic hydroxyapatite crystals (Holtgrane, 1992). This model is proposed for ultrastructural and biochemical analysis of dentin formation in vitro. Transmission electron microscopy will be used to examine morpholizer characteristics of these cells. Extracellular matrix components will be analyzed immunohistochemically and biochemically. Our Specific Aim is to develop a model for studying dentinogensis, and the drugs and growth factors which influence this process for future clinical application.